Stents are well known in the art. They are typically formed of a cylindrical metal mesh, which can expand when pressure is internally applied. Alternatively, they can be formed of wire wrapped into a cylindrical shape or sheets of material formed into a cylindrical shape.
Stents are devices that are usually implanted within bodily conduits including the vascular system to reinforce collapsing, partially occluded, weakened, or abnormally dilated sections of the blood vessel. Stents also have been successfully implanted in other areas, e.g., the urinary tract or the bile duct to reinforce such bodily conduits.
U.S. Pat. No. 4,994,071 (MacGregor) discloses an expandable, bifurcating stent having a main cylindrical lattice formed from interconnected, flexible wire. Two additional cylindrical lattices, having smaller diameters than the main lattice, are similarly constructed. The main lattice includes a flexible wire interconnecting the main lattice to one of the additional lattices. A second flexible wire interconnects the main lattice to the other additional lattice. The flexible wires form backbones that extend axially along the length of the main lattice and along each of the additional lattices. One disadvantage of this bifurcating stent is the complex nature of the interconnection of the flexible wires forming the backbones with the loop structure of each lattice.
Thus, embodiments described in the aforementioned U.S. Pat. No. 6,251,133 provide methods of making a stent which includes a first tubular member having a branch aperture. The tubular member may be inserted in a blood vessel, for example, with the branch aperture aligned with a side branch vessel. A second tubular member having a longitudinal bore may then be disposed and secured within the branch aperture of the first tubular member and, for example, extending into the branch vessel, with the longitudinal bore of the second tubular member in fluid communication with the longitudinal bore of the first tubular member.
Typically, two “over-the-wire” balloon catheters are used for delivering and implanting a bifurcated stent. One of the catheters delivers a portion of the bifurcated stent to the main vessel and the other catheter delivers a portion of the bifurcated to the side branch lumen. Each catheter has a lumen which is dimensioned to receive a guide wire. The guide wires are routed through the vasculature such that the distal end of one of the guide wires extends beyond the target site in the main vessel and the distal end of the other guide wire extends beyond the target site in the side branch lumen. The proximal end of each guide wire is then inserted into the distal end of the guide wire lumen of one of the catheters and the catheters are routed through the vasculature over the guide wires to the target site. When the bifurcated stent portions are positioned within the treatment site, the catheter balloons are inflated and the stent portions are expanded and implanted into the vessel walls. The stent portions may be delivered to and/or implanted at the target site together or sequentially.
The use of two “over-the-wire” catheters with separate guide wires can result in wire crossings within the vasculature which may create confusion to the physician as to which of the guide wires leads to the main vessel and which of the guide wires leads to the side branch lumen. This can result in a significant delay in the procedure. For example, if the catheter carrying the stent portion intended for the main vessel is advanced along the guide wire leading to the side branch lumen, the distal ends of the guide wires must be switched between the main vessel and the side branch lumen or the catheter must be withdrawn from the guide wire and reinserted onto the other guide wire. However, the most serious problem resulting from such wire crossings occurs during the advancement of the two “over-the-wire” catheters on the wires. Specifically, when the two catheters reach the point of a wire crossing, the catheters are positively stopped at that position and cannot be advanced any further along the guide wires. Under these circumstances, the only solution is to withdraw at least one of the guide wires and reposition it within the vasculature. This is both risky and time consuming. Further, when the catheters are advanced toward the treatment site together, the combined profiles of the portions of the catheters with the guide wire lumens may prevent insertion through constricted areas of the vasculature.
One particular delivery method of a bifurcated stent, such as the stents disclosed in U.S. Pat. No. 6,251,133, to the target area includes mounting the stent on two expandable balloons of the same length. Both expandable balloons are advanced along separate guide wires toward the target site together, or are advanced individually in sequential order. One expandable balloon is to be disposed in the main vessel, and one the other is to be disposed in the side branch lumen of the bifurcated vessel. Typically, the side branch balloon is the same length or shorter than the main vessel balloon. Upon reaching the target area in the vessel, the main vessel becomes very crowded due to both balloons filling up the lumen of the main vessel. This causes the tip of the side branch balloon to be pressed against the main vessel, and causes difficulty in orienting the balloon into the side branch lumen, and hinders the ability of the side branch balloon to bend into the side branch vessel.